Precious metal catalysis in organic synthesis, in large measure, has been and continues to be among the most heavily utilized inroads to C—C, C—H and C-heteroatom bond constructions. Chief among these lies palladium chemistry, and with the 2010 Nobel Prizes recognizing Pd-catalyzed Suzuki, Heck and Negishi couplings, even greater use of these and related processes are to be expected.[1] On the other hand, platinoids, in general, are now regarded as “endangered”; that is, the amount of such metals to which there is economical access is finite, and supplies continue to dwindle. Thus, in a sense, award-winning organopalladium chemistry might be viewed as at odds with sustainability. In one aspect, the coupling reactions utilizes micellar catalysis in water and require no organic solvents.
To circumvent this situation, alternative metals have been studied, in particular nickel[2] and copper,[3] especially as applied to the most heavily used Pd-catalyzed cross-coupling: Suzuki-Miyaura reactions.[2a,2e,4] While these have led to varying degrees of success, in the final analysis, Pd remains, by far, the metal of choice. Ideally, technology that accomplishes the desired transformations would do so at the ppm level of palladium. Furthermore, utilization of trace levels of this metal, perhaps as found as an “impurity” in other inexpensive metal salts, would ultimately translate into both a recycling of natural sources of Pd while the cost for its use, therefore, approaches zero.